The histone content of chromatin preparations from leukaemic cells

The histone compositions of chromatin preparations obtained from different adult laukaemias were compared and showed differences between myeloid, monoblastic and lymphoblastic types. The differences were observed whether or not the myeloid precursors were mature or blast forms. Mixing experiments revealed that a potent histone protease was present in the myelocyte chromatin fraction which, unlike most histone proteases, appeared not to be inhibited by serine esterase inhibitors. It is concluded that the differences observed in the histone patterns do not reflect the histon composition present in the cell but are created by proteolytic degradation during the isolation procedures. However, these may still provide some help in identifying myeloblasts in undifferentiated leukaemias.